I have a male normal size betta fish in a bowl and 4 tiger barbs and 2 green scats in a large tank of 40-45 liters
Could anyone say if I leave the betta to the other fishes in the tank, it would harm the tiger barbs or scat.........other wise does tiger harm the betta?

Definitely not a good idea. Firstly, since tiger barbs are nippy, especially when they aren't in a school of 8 or more, they would destroy your betta. Secondly, that tank is massively overstocked. You don't want to be adding another fish in there.